Experimental verification of short-range low-energy carbon-ion scanning in NIRS-HIMAC

Three-dimensional (3D) pencil-beam scanning is an ideal irradiation technique to make the best use of the characteristics of a carbon-ion beam and to provide flexible dose delivery. To suppress beam spread due to multiple scattering and nuclear reactions, we developed a full energy scanning method. In some cases, such as eye treatments, the irradiation fields are very small and short ranged. Accordingly, we prepared a minimum low-energy carbon-ion beam corresponding to water-equivalent residual ranges of less than 2 mm. We performed experimental verification for low-energy carbon-ion beams ranging from 55.6 to 96.0 MeV/u. The accuracy of 3D dose delivery with the low-energy carbon-ion beam was verified by measuring the dose distributions for different target volumes. The results confirmed that the measured dose distributions agree well with the calculated ones. Then, the first eye treatment with low-energy carbon-ion beam to a patient was performed in 2018.